1. Field of the Invention
The present invention pertains to a film drive mechanism that performs winding and rewinding of film housed in a camera, and more particularly to a film drive mechanism that allows the camera to be reduced in size and allows the drive mechanism construction to be simplified.
2. Description of the Related Art
A film drive mechanism using a method in which the film housed in the camera is wound by transmitting the drive power from the motor to the film take-up spool by means of an appropriate reduction mechanism is conventionally known. The film drive mechanism using this type of take-up spool drive method is superior to a mechanism using a method in which the film is wound by transmitting the motor drive power to a sprocket, in that it has a simpler construction and the camera can be made smaller by locating the motor in the space inside the take-up spool Various examples of the prior art as described below have been proposed.
In Japanese Laid-Open Patent Application Sho 62-157018, (hereinafter the `first example of the prior art`), a construction is proposed in which a motor is located inside a take-up spool in a single lens reflex camera, and driving of the mirror drive mechanism, the film winding mechanism, the shutter charging mechanism, etc., are all performed simultaneously by this motor.
In U.S. Pat. No. 5,262,810 (Japanese Laid-Open Patent Application Hei 5-80396) (hereinafter the `second example of the prior art`, a construction is proposed in which the take-up spool contains not only the motor, but also (i) a reduction system that transmits the output of the motor to the take-up spool, and (ii) a sliding clutch mechanism to prevent excessive force from being applied to the film or the reduction system gears when the film is being removed from the film take-up spool.
In Japanese Laid-Open Patent Application Hei 6-317832 (hereinafter the `third example of the prior art`, a construction is disclosed in which the motor is located inside the take-up spool, a reduction system is located outside one end of the take-up spool, and the drive power from the motor is transmitted to the take-up spool by means of the reduction system.
There has been increasing recent demand to make cameras smaller in order to improve their portability, and this, together with the need to further reduce the number of parts in order to achieve the goal, has made it necessary to eliminate dead space in the camera body to the extent possible.
However, because the first example of the prior art is constructed such that it is equipped with, in addition to the motor located inside the take-up spool, an upper unit that has a reduction gear train and is located on the upper part of the take-up spool, as well as a lower unit and a side unit to which the output from the motor is transmitted via a rotation transmission shaft, the height and width of the camera body cannot be reduced.
In the second example of the prior art, the camera body is made compact by locating not only the motor but also the reduction system and the clutch mechanism inside the take-up spool, but because there is no transmission gear mechanism on the take-up spool to externally transmit the motor power, and an essentially round elastic member comprising a part of the sliding clutch mechanism is mounted to the mechanism, it is difficult to add the gear mechanism, and moreover the height of the camera body cannot be reduced due to the existence of the essentially round elastic member.
In the case of the third example of the prior art, while a rewind mechanism is incorporated in the winding mechanism, because only the motor is located inside the take-up spool, and all the gears comprising the reduction system are located outside the take-up spool and are stacked along the axis of the take-up spool it is extremely difficult to reduce the height of the camera body.
As a means to resolve these problems, a mechanism shown in FIG. 6 as a comparison example has been considered, in which a take-up spool 5' is rotatably located inside a spool compartment 3 inside the camera body 1, an electric motor 12 as a drive source and a gear head 13 comprising a reduction system are incorporated in this take-up spool 5', an output gear 6' is mounted to an output shaft 13a that belongs to the gear head 13 and protrudes from the take-up spool 5', a transmission gear 15 located outside the take-up spool 5' engages with the output gear 6', and a spool gear 16 located outside and near the top end of the take-up spool 5' engages with the transmission gear 15, such that the output from the gear head 13 is received by the transmission gear 15, thereby driving the take-up spool 5' from the outside.
Unlike the third example of the prior art, in a non-direct coupling transmission type film drive mechanism of this sort in which the output from the drive source is transmitted to the take-up spool 5' by means of the transmission gear 15, the gear head 13 comprising a reduction system and the electric motor 12 can be located in the space inside the take-up spool and the rewind output to the film housing member in which a film cartridge is placed can be received from the transmission gear 15, while the mechanism offers the further advantage that the height of the camera can be reduced.
However, using this construction, because a space having height al greater than the thickness of the output gear 6' and the spool gear 16 must be located above the spool compartment 3, the height b1 from the center of the camera lens inevitably increases, and consequently not only does the dead space formed at the top of the camera increase, but also the number of parts cannot be reduced.
FIG. 7 shows a construction in which the comparison example of FIG. 6 is further improved The film drive mechanism shown in FIG. 7 is constructed such that, as in the example of FIG. 6, the take-up spool 5' is rotatably located inside the spool compartment 3, the electric motor 12 as a drive source and the gear head 13 are incorporated in this take-up spool 5', the output shaft 13a that belongs to the gear head 13 and protrudes from the take-up spool 5' is connected to a bearing hole 5'b formed in the take-up spool 5' by means of a key 14, the output gear 6' is pressed against and engaged with the output shaft 13a of the gear head 13, and an initial gear 8e of the transmission gear train located outside the take-up spool is engaged with the output gear 6'.
In this construction, the output from the gear head 13 is directly transmitted to the take-up spool 5' via the key 14 and the output to the film housing member is received from the output gear 6', which offers the advantage over the non-direct coupling transmission type mechanism shown in FIG. 6 that the amount of dead space above the spool compartment can be reduced.
However, because the output gear 6' is pressed against the output shaft 13a of the gear head 13, the output gear 6' must be a separate member from the take-up spool 5', and because there must be a space having the height a2 above the spool compartment 3 that is larger than the thickness of the output gear 6' because it has to accommodate the length of the engagement between the bearing hole 5'b of the take-up spool 5' and the key 14 and the space in which the output gear 6' is inserted, the height b2 from the center of the lens of the camera body 1 inevitably increases. Therefore, there is a limit to the extent to which the amount of dead space can be reduced.